Ban Ki-moon says he has received "alarming news" that Assad may use chemical weapons, warns Assad against escalation.

UN Secretary-General Ban Ki-moon said on Friday he was not aware of any confirmed reports that Syrian President Bashar Assad was preparing to use chemical weapons but that if he did so it would be an "outrageous crime."

Several Western countries have issued warnings this week to Assad's government not to use chemical arms, many citing intelligence that Washington has said showed it might be preparing to use poison gas.

"Recently we have been receiving alarming news that the Syrian government may be preparing to use chemical weapons. We have no confirmed reports on this matter," UN chief Ban said after visiting a Syrian refugee camp in Turkey.

"However, if it is the case, then it will be an outrageous crime in the name of humanity," he said. "I know that many world leaders have added their voices urging him not to use it and warning him that it will create huge consequences."

Ban said he had spoken on Thursday with the head of the Organization for the Prohibition of Chemical Weapons about ways to investigate the reports but no concrete plan had yet emerged.

He called on world powers and the UN Security Council to unite and take action to end the Syrian conflict, saying only a political solution could stop the bloodshed. But he said the international community had not yet started to discuss the possibility of arranging safe passage for Assad and his family out of Syria should he be persuaded to leave.

Earlier this week, Prime Minster Binyamin Netanyahu addressed raised concerns that Syrian President Bashar Assad could be preparing to use chemical weapons in his fight to survive against opposition forces, stating that Israel was monitoring the situation closely. "These weapons cannot be used or transferred to terrorist organizations," Netanyahu said.

Israel has also asked Jordan on a number of occasions for “permission” to bomb Syrian chemical weapons sites, according to a report published earlier this week by The Atlantic, citing intelligence sources in both countries.